Vast amounts of information are conveyed by our faces – not just speech, but also nonverbal information – through our expressions. It’s also very important that we can tell the difference between people. Psychologists have suggested that our minds have, or learn, very specific abilities to process faces, their features and the information they convey.

Now, this ability is ‘tuned’ to work best on upright faces (not surprisingly, as that’s the way we usually see them). So when a face is turned upside down some of these processes don’t work so well, especially the ones that tell us about the spatial relationships between the main parts of the face: the mouth, eyes and nose. So when the face is upside down – it’s as if these abilities get turned off and so we don’t spot the oddities.

We know that very specific bits of our brains do this job – because people with prosopagnosia (where part of the brain is damaged) can’t spot the difference between the upside-down faces and the ones that are the right way up.